Surgical stapler having cartridge with adjustable cam mechanism

ABSTRACT

A surgical fastener applying apparatus comprising a cartridge section having a cartridge containing a plurality of fasteners and an anvil section having an anvil for receiving the fasteners when advanced from the cartridge. The cartridge and anvil sections clamp tissue therebetween. A cam member is slidable within the cartridge section to fire the fasteners, and is movable from a first position defining a first distance from the anvil to a second position defining a second different distance from the anvil. A cam adjusting member is operably associated with the cam member and moves the cam member from the first position to the second position in response to a thickness of tissue clamped between the anvil and cartridge sections.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 12/899,155 filed Oct. 6, 2010, now U.S. Pat. No. 8,418,907, which claims benefit of Provisional application No. 61/258,246 filed Nov. 5, 2009, and the disclosures of each of the above-identified applications are hereby incorporated by reference in their entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a surgical stapling device and more particularly to a surgical stapling device having an adjustable staple firing mechanism.

2. Background of the Related Art

There are several known types of surgical stapling instruments specifically adapted for use in various procedures. In many such surgical devices, tissue is first grasped or clamped between opposing jaw structures and then joined by surgical fasteners. The fasteners are typically in the form of surgical staples. These staples generally include a pair of legs adapted to penetrate tissue and connected by a backspan from which they extend. In use, the staples are formed to a “B” configuration. Two-part fasteners are also known and include legs that are barbed and connected by a backspan which are engaged and locked into a separate retainer piece that is usually located in the anvil. In some devices, a knife is provided to cut the tissue which has been joined by the fasteners.

In these devices, one of the jaw structures carries a staple cartridge having one or more laterally spaced rows of staples, which are aligned with corresponding rows of anvil depressions on an opposing jaw structure. The tissue is initially gripped or clamped such that individual staples can be ejected from the cartridge, through the slots, and forced through the clamped tissue. The staples are ejected by longitudinal movement of a driver and forced through the clamped tissue, forming against the staple forming depressions of the anvil. The staples can be arranged in a linear or non-linear row.

A common issue in transecting tissue and/or in anastomosis procedures employing the surgical stapling instruments is the balance between anastomotic strength and the degree of hemostasis achievable. It is known to include different size staples in a surgical stapling instrument having a constant gap (uniform distance) between an anvil and a staple cartridge.

A common concern in these surgical procedures is hemostasis, or the rate at which bleeding of the target tissue is stopped. It is commonly known that by increasing the amount of pressure applied to a wound, the flow of blood can be limited, thereby decreasing the time necessary to achieve hemostasis. To this end, conventional surgical fastening apparatus generally apply two or more rows of fasteners about the cut-line to compress the surrounding tissue in an effort to stop any bleeding and to join the cut tissue together. Each of the fasteners will generally apply a compressive force to the tissue sufficient to effectuate hemostasis, however, if too much pressure is applied, this can result in a needless reduction in blood flow to the tissue surrounding the cut-line. Accordingly, the joining of tissue together in this manner may result in an elevated level of necrosis, a slower rate of healing, and/or a greater convalescence. On the other hand, if not enough pressure is applied, proper hemostasis may not be achieved.

Consequently, it would be advantageous to provide a surgical fastening apparatus capable of adjusting the application of staples to accommodate different tissue thicknesses.

SUMMARY

The present disclosure relates to camming members adjustable to different levels depending on tissue thickness. In one aspect, the present disclosure provides a surgical fastener applying apparatus comprising a cartridge section having a cartridge containing a plurality of fasteners and an anvil section having an anvil for receiving the fasteners when advanced from the cartridge. The cartridge and anvil sections clamp tissue therebetween. A cam member is slidable within the cartridge section to fire the fasteners, and has a first position defining a first distance from the anvil section and movable to a second position defining a second different distance from the anvil section. A cam adjusting member operably associated with the cam member moves the cam member from the first position to the second position in response to a thickness of tissue clamped between the anvil and cartridge sections.

In another aspect, a surgical fastener applying apparatus is provided comprising a cartridge section having a cartridge containing a plurality of fasteners and having a tissue contacting surface and an anvil section having an anvil for receiving the fasteners when advanced from the cartridge. The cartridge and anvil sections clamp tissue therebetween. A cam member is movable between a first position defining a first distance from the tissue contacting surface of the cartridge and a second position defining a second position defining a second different distance from the tissue contacting surface. The cam member is automatically movable from the first position to the second position in response to the thickness of tissue clamped between the anvil and cartridge sections.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present disclosure are described hereinbelow with references to the drawings, wherein:

FIG. 1 is a perspective view of one embodiment of the surgical stapler having a fastener firing mechanism of the present disclosure;

FIG. 2 is an exploded view of a cartridge assembly of the present disclosure including a portion of the firing mechanism;

FIG. 3 is a close up view of the cam members and cam adjustment assembly of FIG. 2;

FIG. 4 is a transverse cross-sectional view of a portion of the cartridge assembly showing the cam members at a first position for application of staples to thinner tissue;

FIG. 5 is a transverse cross-sectional view of the cartridge and anvil assemblies showing the cam members at the position of FIG. 4 and the cartridge and anvil clamping the tissue, prior to firing of the staples;

FIG. 6 is a view of a portion of the cartridge and anvil assemblies in partial cross section illustrating the cam member in the position of FIG. 4 and in the pre-fired position before contact with a staple pusher;

FIG. 7 is a cross-sectional view similar to FIG. 5 showing advancement of the staples through body tissue and into contact with anvil pockets of the anvil assembly;

FIG. 8 is a view similar to FIG. 6 showing advancement of the cam member into contact with the staple pusher to advance the staple for deformation against the anvil;

FIG. 9 illustrates the staple formed around a thinner tissue section corresponding to the position of the cam members in FIGS. 4-8;

FIG. 10 is a transverse cross-sectional view of the cartridge and anvil assemblies similar to FIG. 7 showing the cam members in a second position for application of staples to thicker tissue;

FIG. 11 is a view of a portion the cartridge and anvil assemblies in partial cross section illustrating the cam member in the position of FIG. 10 and showing advancement of the cam member into contact with the staple pusher to advance the staple for deformation against the anvil;

FIG. 12 illustrates the staple formed around a thicker tissue section corresponding to the position of the cam members in FIGS. 10 and 11;

FIG. 13 is a transverse cross-sectional view of the cartridge and anvil assemblies similar to FIG. 10 showing the cam members in a third position for application of staples to even thicker tissue;

FIG. 14 is a view of a portion of the cartridge and anvil assemblies in partial cross section illustrating the cam member in the position of FIG. 13 and showing advancement of the cam member into contact with the stapler pusher to advance the staple for deformation against the anvil;

FIG. 15 illustrates the staple formed around a thicker tissue section corresponding to the position of the cam members in FIGS. 13 and 14;

FIG. 16 is an exploded view of the cam members and cam adjustment assembly of an alternate embodiment of the present disclosure;

FIG. 17 is a transverse cross-sectional view of a portion of the cartridge assembly of the embodiment of FIG. 16 showing the cam member at a first position for application of staples to thinner tissue;

FIG. 18 is a view similar to FIG. 17 showing the cam member at another position for application of staples to thicker tissue;

FIG. 19 is a perspective view of another surgical stapler having a fastener firing mechanism of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the presently disclosed stapler will now be described in detail with reference to the drawings wherein like numerals designate identical or corresponding elements in each of the several views. As is common, the term “proximal” refers to that part or component closer to the user or operator, i.e. surgeon or physician, while the term “distal” refers to that part or component further away from the user.

FIG. 1 illustrates one type of surgical stapler that can incorporate the cam bar/pusher arrangement of the present disclosure. The surgical stapler 10 has a cartridge half section 12, an anvil half section 14, and handles 15 and 16 for facilitating clamping of the sections 12 and 14. Cartridge half section 12 has a channel 47 (FIG. 2) to receive cartridge 32 which includes a plurality of staples 60 and a plurality of staple pushers 36 to advance the staples 60 from the cartridge 32 through slots 52.

The staple firing mechanism includes a cam bar assembly which is advanced by distal advancement of manual firing lever 28 (FIG. 1). The cam bar assembly is slidable for longitudinal advancement in the cartridge 32 to advance the pushers 36 in a direction substantially transverse to the longitudinal axis of the stapler and substantially transverse to the direction of movement of the camming members. Engagement of the pushers 36 by the cam members advances the staples 60 through the tissue and into contact with the anvil depressions (pockets) 22 (FIG. 5) of the anvil half section 14. In the illustrated embodiment of FIG. 2, there are two staggered linear rows of staple slots 52 formed on either side of a knife slot 58 which guides a knife bar 50 with knife blade 51 between the rows of staples 60. A different number of rows can be provided and a knife can optionally not be provided. A single staple 60 is positioned in each of the slots 52. Staple pushers 36 are aligned with each slot 52 so that preferably a single staple pusher 36 is positioned under the staple 60 retained in the slot 52. The pushers 36 can optionally be attached to each other in groups of two offset oriented pusher pairs. More details of the stapler are disclosed in U.S. Pat. No. 7,140,527, issued Nov. 28, 2006, and U.S. Pat. No. 7,055,730, issued Jan. 6, 2006, the entire contents of each of these applications are incorporated herein by reference.

With reference to FIGS. 2 and 3, the cam member arrangement of the present disclosure will now be described. Cam member support or sled 38 includes a pair of outer camming elements 39 a and a pair of inner camming elements 39 b. An upper pair of projecting ribs or teeth 56 a (only one of which is shown in the view of FIG. 3) are positioned on opposing sides of the support 38. A lower pair of ribs or teeth 56 b (only one of which is shown in the view of FIG. 3) are positioned on opposing sides of the support 38. The outer camming elements 39 a and inner camming elements 39 b are preferably axially staggered as shown, i.e. the inner camming elements 39 b are positioned slightly distally of outer camming elements 39 a.

Cam adjusting members 34 and 35 extend through slots 54 a 54 b, respectively in cartridge 32 and are biased upwardly (toward tissue contacting surface 33 of cartridge 32) by springs 36 a, 36 b and 37 a, 37 b, respectively. Cam adjusting member 35 has a projecting tab 35 a at a proximal end engageable with pivot arm 48. Cam adjusting member 34 has a projecting tab 34 a at a proximal end for engagement with pivot arm 42. The opposite surface (upper surface as viewed in the orientation of FIG. 2) of cam adjusting member 35 has a tissue contacting surface 35 b with an extended planar surface forming a T-shape. Similarly, the opposite surface of cam adjusting member 34 has a tissue contacting surface 34 b forming a T-shape. The surfaces 34 b, 35 b come into contact with and compress the tissue when the anvil and cartridge sections 14, 12 are approximated to clamp tissue therebetween.

The cam adjusting members 34, 35 adjust in the distance they protrude from the slots 54 a, 54 b, depending on tissue thickness. This can be seen for example by comparing FIGS. 5, 10 and 13. When the tissue is relatively thin as shown in FIG. 5, the cam adjusting members 34, 35 will protrude a distance X beyond the tissue contacting surface 33 of cartridge 32. When encountering thicker tissue clamped between the cartridge and anvil sections 12, 14 as in FIG. 10, the cam adjusting members 34, 35 will protrude a shorter distance Y from the tissue contacting surface 33 of the cartridge 32. In FIG. 13, even thicker tissue is encountered such that the cam adjusting members 34, 35 barely protrude from the slots 54 a, 54 b as the T-surfaces 34 b, 35 b are positioned on the tissue contacting surface 33. As can be appreciated, as thicker tissue is encountered and clamped between the anvil 20 and cartridge 32, the clamped tissue applies an inward force toward the cartridge 32 (or downward as viewed in the orientation of FIGS. 5, 10 and 13) on the T surface 34 b, 35 b of cam adjusting members 34, 35. Such downward force causes pivot arms 42, 41 and 48, 40 to pivot to change the pusher contact position of the cam elements 39 a, 39 b as described in detail below. As can be appreciated, the terms upward and downward refer to the orientation of the stapler/components shown in the Figures, it being understood that if the orientation of the stapler/components changes, the upward and downward references would likewise change.

With reference to FIGS. 3, 4 and 5, pivot arm 42 has an outer region 42 a which is in contact with a lower surface of tab 34 a of camming element 34. In the normal position, the cam adjustment element 34 is in its upward position with surface 34 furthest from the tissue contacting surface 33 of cartridge 32 due to the biasing force of springs 36 a, 36 b. First pivot arm 42 engages second pivot arm 41 which is attached to, or alternatively in abutment with, the sled 38 at inner region 41 b. When surface 42 a of tab 34 forces inner region 42 a of pivot arm 42 downwardly, pivot arm 42 pivots about pin 42 c (counterclockwise as viewed in FIG. 5). Such pivotal movement causes inner region 42 d to engage outer region 41 d of second pivot arm 41, causing arm 41 to pivot about pin 41 c (clockwise as viewed in FIG. 5) so that inner region 41 b is forced in a direction toward the sled 38 (downwardly as viewed in the orientation of FIG. 5). Such movement of inner region 41 b forces sled 38 in a direction away from the tissue contacting surface 33 (downwardly as viewed in FIGS. 4 and 5). This changes the plane in which the sled 38 travels to contact the staple pushers 36. Ribs 56 a, 56 b of sled 48 are forced out of the upper retaining or locking recesses 49 a, 49 b formed in the inner wall of cartridge 32 and are moved to engage different (lower) retaining recesses at a different “level” of the sled 38.

Similarly, with reference to FIGS. 3 and 5, first pivot arm 48 has an outer region 48 a which is in contact with a surface of tab 35 a of cam adjustment member 35. In the normal position, cam adjustment member 35 is in its upward position with tissue engagement surface 35 b furthest from tissue contacting surface 33 of cartridge 32 due to the biasing force of springs 37 a, 37 b. First pivot arm 48 engages second pivot arm 40 which is attached to, or alternatively in abutment with, the sled 38 at inner region 40 b. When outer region 48 a is forced downwardly by tab 34 a, first pivot arm 48 is pivoted about pin 48 c (clockwise as viewed in FIG. 5) such that inner region 48 c engages outer region 40 d of second pivot arm 40. This forces arm 40 to pivot about pin 40 c (counterclockwise as viewed in FIG. 5), causing inner region 40 b to apply a downward force to sled 38, thereby forcing sled 38 in a direction away from the tissue contacting surface 33 (downwardly as viewed in FIG. 5). This, in conjunction with pivot arms 41, 42 changes the plane in which the sled 38 travels to contact the staple pushers 36. Ribs 56 a, 56 b are forced out of the retaining or locking recesses 46 a, 46 b and 49 a, 49 b formed in the inner wall of cartridge 32 and moved to engage different (lower) locking recesses e.g. recesses 46 c, 46 d and 49 c, 49 d. This different position is shown in FIG. 10.

In FIG. 13, the first pivot arms 48, 41 have pivoted even further, due to the force of the thicker tissue on cam adjusting members 34, 35, causing respective second pivot arms 41, 40 to pivot further, applying an additional force on the sled 38, thereby forcing it further from tissue contacting surface 33 than in FIG. 10, with the ribs 56 a, 56 b engaging lower recesses 46 e, 46 f and 49 e, 49 f of the cartridge 32. As can be appreciated, when the sled 38 is closer to the tissue contacting surface 33, (for thinner tissue) the camming elements 39 a, 39 b are closer to the staple pushers 36 so that their advancement will force the staples further out from the respective slots 52 into engagement with the anvil. This is shown in FIGS. 6, 8 and 9 where the staple 60 forms a smaller tissue enclosure area, e.g. a tighter B shape. When the sled 38 is further from the staple pushers 36 due to thicker tissue, the camming elements 39 a, 39 b are further from the staple pushers 36, due to the changed position (level) of the sled 38, and thus the angled camming surfaces contact the pushers 36 at a different (lower) region. Thus, the staples 60 will form with a larger tissue enclosure space as shown in FIGS. 11 and 12. When even thicker tissue is encountered, the camming elements 39 a, 39 b will be located even a further distance from staple pushers 36, contacting the pushers at a still lower region, so that the staples 60 will form an even larger tissue enclosure area to accommodate the thicker tissue. This is illustrated in FIGS. 14 and 15. Stated another way, the angled camming surfaces 55 a, 55 b of the camming elements 39 a, 39 b will contact a different curved contacting region of the staple pushers 36, depending on the position (level) of sled 38 with respect to the pushers 36 of cartridge 32.

FIG. 16-18 illustrate an alternate embodiment of the present disclosure for adjusting the plane of the sled and camming elements. In this embodiment, a linkage mechanism is provided to adjust the “level” of the sled in response to tissue thickness. More specifically, a sled 138 has a pair of outer camming elements 139 a and a pair of inner camming elements 139 b, having respective angled camming surfaces 155 a, 155 b, configured for engagement with staple pushers to advance staples out of the cartridge in the same manner as described above with the embodiment of FIGS. 1-15. The linkage mechanism includes a rocker arm 162, a pivot arm 160 with an arcuate region 161 and a connector 165. Rocker 162 has a transverse aperture 162 a to receive locking pin 164 which also extends through opening 165 a in connector 165. The curved outer surface 165 b of connector 165 is seated within arcuate region 161 of pivot arm 160. Curved end 162 b of rocker 162 is received within opening 134 c of tab 134 a of cam adjusting element 134.

Similarly, pivot arm 170 has an arcuate region 171. Rocker 172 has a transverse aperture 172 a to receive locking pin 174 which also extends through opening 175 a in connector 175. The curved outer surface 175 b of connector 175 is seated within arcuate region 171 of pivot arm 170. Curved end 172 b of rocker 172 is received within an opening of a tab of a second cam adjusting member (not shown) identical to cam adjusting member 134.

Sled 138 has ribs or teeth 156 a, 156 b on opposing sides which are identical in structure and function to the ribs 56 a, 56 b of sled 38 of FIG. 2 and engages locking recesses in the cartridge to retain the sled in its radial position in the same manner as described above with sled 38. In use, sled 138 is automatically adjustable based on the tissue thickness. This occurs as the cam adjusting members are forced away from the tissue contacting surface of the cartridge when encountering thicker tissue (in the same manner as described above for cam adjusting members 34, 35). When forced away from the tissue contacting surface of the cartridge, they apply an inward force (downwardly in the orientation of FIGS. 16-18) on rockers 162 (and rocker 172), causing it to pivot as seen in FIG. 18. Note FIGS. 17 and 18 show movement of one of the linkage mechanisms (rocker 162, pivot arm 160, etc.), it being understood that rocker 172, pivot arm 170 and connector 175 of the other linkage mechanism operates in a similar manner. This pivoting of the rocker 162 forces connector 165 upwardly, forcing the end 167 of pivot arm 160 upwardly so that it rotates clockwise about the support pin 174 so the inner end 169 (attached to or abutting sled 138) applies a downward force on the sled 138. For brevity, only the two extreme positions of the sled 138 are shown, with FIG. 17 showing the sled 138 in its uppermost position, closest to the tissue contacting surface of the cartridge for thinner tissue, and FIG. 18 showing the sled 138 in its lowermost position, furthest from the tissue contacting surface of the cartridge to adjust for thicker tissue. Note spring 170, connector 175, and rocker 172 act in a similar manner to adjust the position of the sled 18, applying a force on a second region of the sled by end 179 (FIG. 16) of pivot arm 170 which is attached to or in abutment with sled 138.

As can be appreciated with reference to the Figures, the difference in location or “level” of the sled 38, 138, i.e. position on different planes, enables the instrument to automatically adjust to tissue of different thickness. That is, the tissue thickness itself dictates the position of the cam adjustment members which in turn controls the position of the sled 38, 138. The position of the sled 38, 138 in turn affects the extent of deployment of the staples 60 due to the varied position of the angled camming surfaces of the camming members 39 a, 39 b, 139 a, 139 b which contact the staple pushers. Accordingly, the extent of staple deployment is automatically determined by the tissue thickness.

It should be appreciated that although three discrete positions of the sled are illustrated, a different number of positions are contemplated, including an infinite number of variations of the planes of the sled.

It should be appreciated that the adjustable planes for the camming elements of the present disclosure can also be used with other staplers, including, but not limited to other linear staples and endoscopic linear staplers. This cam arrangement can be used for example with the endoscopic surgical stapler 200 of FIG. 19, which has an elongated tubular portion 212, an anvil assembly 214 pivotally mounted at a distal end portion of the elongated tubular portion 212 and a cartridge assembly 220. The anvil and cartridge assemblies 214, 220 are moved into approximation to clamp tissue therebetween. A handle 230 is squeezed to clamp the anvil and fire the staples in the manner disclosed in U.S. Pat. Nos. 5,762,256 and 5,865,361, the entire contents of which are incorporated by reference.

Although described for fastener applying apparatus for firing staples formed by an anvil, the camming elements of this disclosure could also be used in fastener applying apparatus for firing two part fasteners.

While the above description contains many specifics, these specifics should not be construed as limitations on the scope of the present disclosure, but merely as illustrations of various embodiments thereof. Therefore, the above description should not be construed as limiting, but merely as exemplifications of various embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the disclosure. 

What is claimed is:
 1. A surgical stapling device, comprising: a cartridge section defining a longitudinal axis and having a cartridge containing a plurality of fasteners; an anvil section, the cartridge section and the anvil section configured to clamp tissue therebetween; and a cam member slidable through the cartridge section in a direction parallel to the longitudinal axis and configured to automatically change its levels in response to a thickness of tissue clamped between the cartridge and anvil sections before it slides through the cartridge section and to maintain a level while sliding through the cartridge section.
 2. The surgical stapling device of claim 1, wherein the cam member engages a plurality of pushers at a different contact area in response to the thickness of tissue clamped between the cartridge and anvil sections.
 3. The surgical stapling device of claim 2, wherein each of the plurality of pushers engages a fastener of the plurality of fasteners to advance the fastener from the cartridge, through the tissue clamped between the cartridge and anvil sections, and against an anvil pocket of a plurality of anvil pockets in the anvil section to form each fastener with an equal tissue enclosure space.
 4. The surgical stapling device of claim 3, wherein the tissue enclosure space of each staple corresponds to the level of the cam member.
 5. The surgical stapling device of claim 1, wherein the cam member has a plurality of projections to retain the cam member in one of a plurality of levels.
 6. The surgical stapling device of claim 1, further including a cam adjusting member operably associated with the cam member, the cam adjusting member moving the cam member from a first level to a second level in response to the thickness of tissue clamped between the cartridge section and the anvil section.
 7. The surgical stapling device of claim 6, wherein the second level is different from the first level.
 8. The surgical stapling device of claim 6, wherein the cam adjusting member is spring biased toward the anvil section.
 9. The surgical stapling device of claim 8, wherein the cam adjusting member is forced away from the anvil section against the spring bias in response to the tissue clamped between the cartridge section and the anvil section.
 10. The surgical stapling device of claim 6, further including first and second pivoting members, the first and second pivoting members interposed between the cam member and the cam adjusting member.
 11. A surgical stapling device, comprising: a cartridge section having a cartridge defining a longitudinal axis and containing a plurality of fasteners; an anvil section, the cartridge section and the anvil section configured to clamp tissue therebetween; a cam member slidable within the cartridge section and configured to automatically move transverse to the longitudinal axis of the cartridge among a plurality of levels to form fasteners with a tissue enclosure space corresponding to a thickness of tissue clamped between the cartridge and anvil sections; and a cam adjusting member operably associated with the cam member, the cam adjusting member moving the cam member from a first level to a second level in response to the thickness of tissue clamped between the cartridge section and the anvil section; the cam adjusting member having an extended planar tissue contacting surface.
 12. The surgical stapling device of claim 6, wherein the cam adjusting member engages a pivotable element in response to the thickness of tissue clamped between the cartridge section and the anvil section.
 13. A surgical stapling device, comprising: a cartridge section having a cartridge defining a longitudinal axis and containing a plurality of fasteners; an anvil section, the cartridge section and the anvil section configured to clamp tissue therebetween; a cam member slidable within the cartridge section and configured to automatically move transverse to the longitudinal axis of the cartridge among a plurality of levels to form fasteners with a tissue enclosure space corresponding to a thickness of tissue clamped between the cartridge and anvil sections; and a cam adjusting member operably associated with the cam member, the cam adjusting member moving the cam member from a first level to a second level in response to the thickness of tissue clamped between the cartridge section and the anvil section, the cam adjusting member engaging a pivotable element in response to the thickness of tissue clamped between the cartridge section and the anvil section, the pivotable element is operatively associated with a pivoting arm that applies a force to the cam member in a direction away from a tissue contacting surface of the cartridge. 